Bottom Line:
Moreover, concomitant incubation of AA with PA dose-dependently attenuated the detrimental effects of the saturated fatty acid, so reducing apoptosis and decreasing parameters of oxidative stress [ROS (reactive oxygen species) and NO levels] while improving the GSH/GSSG ratio.AA decreased the protein expression of iNOS (inducible NO synthase), the p65 subunit of NF-κB (nuclear factor κB) and the p47 subunit of NADPH oxidase in PA-treated cells.These findings indicate that AA has an important regulatory and protective β-cell action, which may be beneficial to function and survival in the 'lipotoxic' environment commonly associated with Type 2 diabetes mellitus.

ABSTRACTChronic exposure of pancreatic β-cells to saturated non-esterified fatty acids can lead to inhibition of insulin secretion and apoptosis. Several previous studies have demonstrated that saturated fatty acids such as PA (palmitic acid) are detrimental to β-cell function compared with unsaturated fatty acids. In the present study, we describe the effect of the polyunsaturated AA (arachidonic acid) on the function of the clonal pancreatic β-cell line BRIN-BD11 and demonstrate AA-dependent attenuation of PA effects. When added to β-cell incubations at 100 μM, AA can stimulate cell proliferation and chronic (24 h) basal insulin secretion. Microarray analysis and/or real-time PCR indicated significant AA-dependent up-regulation of genes involved in proliferation and fatty acid metabolism [e.g. Angptl (angiopoietin-like protein 4), Ech1 (peroxisomal Δ3,5,Δ2,4-dienoyl-CoA isomerase), Cox-1 (cyclo-oxygenase-1) and Cox-2, P<0.05]. Experiments using specific COX and LOX (lipoxygenase) inhibitors demonstrated the importance of COX-1 activity for acute (20 min) stimulation of insulin secretion, suggesting that AA metabolites may be responsible for the insulinotropic effects. Moreover, concomitant incubation of AA with PA dose-dependently attenuated the detrimental effects of the saturated fatty acid, so reducing apoptosis and decreasing parameters of oxidative stress [ROS (reactive oxygen species) and NO levels] while improving the GSH/GSSG ratio. AA decreased the protein expression of iNOS (inducible NO synthase), the p65 subunit of NF-κB (nuclear factor κB) and the p47 subunit of NADPH oxidase in PA-treated cells. These findings indicate that AA has an important regulatory and protective β-cell action, which may be beneficial to function and survival in the 'lipotoxic' environment commonly associated with Type 2 diabetes mellitus.

Figure 4: Effect of COX/LOX inhibitors in combination with AA on insulin secretionBRIN-BD11 β-cells were incubated in the absence (Ctrl) or presence of 100 μM AA or 100 μM AA in combination with 100 μM acetaminophen (Acet) or 100 μM indomethacin (Indo) or 100 μM NS-398 or 10 μM SC-560 for 24 h. Subsequently, an acute (20 min) determination of basal- and nutrient- (D-glucose and L-alanine) stimulated insulin secretion was obtained. Results are expressed as means±S.E.M. for six independent experiments. *P<0.05 and **P<0.01 compared with cells incubated with control medium; #P<0.05 and ##P<0.01 compared with cells incubated with 100 μM AA and stimulated with 16.7 mM D-glucose and 10 mM L-alanine.

Mentions:
In order to determine whether the effects of AA on β-cell function were mediated by the products of AA metabolism or by AA itself, specific COX enzyme inhibitors and a non-selective LOX enzyme inhibitor were added to the cell culture medium for 24 h prior to the determination of acute nutrient stimulated insulin secretion (Figure 4). The selectivity of various COX inhibitors has recently been reviewed [24].

Figure 4: Effect of COX/LOX inhibitors in combination with AA on insulin secretionBRIN-BD11 β-cells were incubated in the absence (Ctrl) or presence of 100 μM AA or 100 μM AA in combination with 100 μM acetaminophen (Acet) or 100 μM indomethacin (Indo) or 100 μM NS-398 or 10 μM SC-560 for 24 h. Subsequently, an acute (20 min) determination of basal- and nutrient- (D-glucose and L-alanine) stimulated insulin secretion was obtained. Results are expressed as means±S.E.M. for six independent experiments. *P<0.05 and **P<0.01 compared with cells incubated with control medium; #P<0.05 and ##P<0.01 compared with cells incubated with 100 μM AA and stimulated with 16.7 mM D-glucose and 10 mM L-alanine.

Mentions:
In order to determine whether the effects of AA on β-cell function were mediated by the products of AA metabolism or by AA itself, specific COX enzyme inhibitors and a non-selective LOX enzyme inhibitor were added to the cell culture medium for 24 h prior to the determination of acute nutrient stimulated insulin secretion (Figure 4). The selectivity of various COX inhibitors has recently been reviewed [24].

Bottom Line:
Moreover, concomitant incubation of AA with PA dose-dependently attenuated the detrimental effects of the saturated fatty acid, so reducing apoptosis and decreasing parameters of oxidative stress [ROS (reactive oxygen species) and NO levels] while improving the GSH/GSSG ratio.AA decreased the protein expression of iNOS (inducible NO synthase), the p65 subunit of NF-κB (nuclear factor κB) and the p47 subunit of NADPH oxidase in PA-treated cells.These findings indicate that AA has an important regulatory and protective β-cell action, which may be beneficial to function and survival in the 'lipotoxic' environment commonly associated with Type 2 diabetes mellitus.

ABSTRACTChronic exposure of pancreatic β-cells to saturated non-esterified fatty acids can lead to inhibition of insulin secretion and apoptosis. Several previous studies have demonstrated that saturated fatty acids such as PA (palmitic acid) are detrimental to β-cell function compared with unsaturated fatty acids. In the present study, we describe the effect of the polyunsaturated AA (arachidonic acid) on the function of the clonal pancreatic β-cell line BRIN-BD11 and demonstrate AA-dependent attenuation of PA effects. When added to β-cell incubations at 100 μM, AA can stimulate cell proliferation and chronic (24 h) basal insulin secretion. Microarray analysis and/or real-time PCR indicated significant AA-dependent up-regulation of genes involved in proliferation and fatty acid metabolism [e.g. Angptl (angiopoietin-like protein 4), Ech1 (peroxisomal Δ3,5,Δ2,4-dienoyl-CoA isomerase), Cox-1 (cyclo-oxygenase-1) and Cox-2, P<0.05]. Experiments using specific COX and LOX (lipoxygenase) inhibitors demonstrated the importance of COX-1 activity for acute (20 min) stimulation of insulin secretion, suggesting that AA metabolites may be responsible for the insulinotropic effects. Moreover, concomitant incubation of AA with PA dose-dependently attenuated the detrimental effects of the saturated fatty acid, so reducing apoptosis and decreasing parameters of oxidative stress [ROS (reactive oxygen species) and NO levels] while improving the GSH/GSSG ratio. AA decreased the protein expression of iNOS (inducible NO synthase), the p65 subunit of NF-κB (nuclear factor κB) and the p47 subunit of NADPH oxidase in PA-treated cells. These findings indicate that AA has an important regulatory and protective β-cell action, which may be beneficial to function and survival in the 'lipotoxic' environment commonly associated with Type 2 diabetes mellitus.